This document discusses collaboration models for sustainability at universities. It provides examples of collaboration within a university, within a city/state, and with global partners. For intra-university collaboration, it discusses engaging different university departments and student groups. The case study of Yale University details their department-level sustainability plans. For local collaboration, it outlines partnering with industry, government, and NGOs, as seen in EPFL's solar energy project. The case study of the University of Milan collaborating with Politecnico of Milan on sustainability initiatives is also provided. The document addresses how collaboration models may evolve and questions to consider when defining new models. It also outlines challenges to overcome, such as creating urgency and short-term wins.